1. Field of the Invention
This invention relates to a novel optical information recording medium and the recording of information thereon. More particularly, the present invention relates to an information recording medium, preferably in the form of a disk, suitable for use with optical recording and playback apparatus, which recording medium comprises as the information layer a microporous polymeric layer coated with a polymeric film. The present invention also relates generally to an optical recording medium used in the form of a tape or as a strip on a card wherein the medium comprises a coated microporous polymeric layer.
2. Description of the Prior Art
Various optical recording media and methods for recording information thereon are known to the prior art. For example, optical recording methods in which light from a laser or some other suitable light source is focused upon the surface of a recording medium with sufficient intensity to cause the formation of pits in the surface material have been proposed. In such methods, an information representative pattern of pits is formed in the surface of the recording medium by suitable control of the intensity of the focused light in accordance with the information to be recorded, while relative motion is established between the recording medium and the focused light spot.
In recent years, attention has been increasingly paid to the information recording method in which information is written in a thin film of metal or the like formed on a substrate by using a laser ray or beam. According to such a method, the recording of information has been accomplished by forming holes or recesses in the metallic thin film under the action of a thermal energy beam such as a laser ray. See, e.g., U.S. Pat. No. 4,238,803.
Spong, U.S. Pat. No. 4,097,895, describes a recording medium which comprises a light reflecting material, such as aluminum or gold, coated with a light absorbing layer, such as fluorescein, which is operative with an argon laser light source. The thickness of the light absorbing layer is chosen so that the structure has minimum reflectivity. An incident light beam then ablates, vaporizes or melts the light absorbing layer, leaving a hole and exposing the light reflecting layer. After recording at the wavelength of the recording light, maximum contrast between the minimum reflectance of the light absorbing layer and the reflectance of the light reflecting layer exists. In this regard, note also U.S. Pat. No. 4,219,826.
Carlson, in U.S. Pat. No. 3,475,760, discloses a system for directly recording information in a thermoplastic film as a deformation by using a high energy laser scanning beam of small diameter.
It has also recently been proposed to employ in an optical disk a thermodegradable layer upon which is deposited a metallic layer which is absorbent at the wavelength of the inscription radiation. See, for example, U.S. Pat. No. 4,380,016. Upon irradiation, the deposited metallic layer heats up, with the heat being diffused towards the thermodegradable layer. The thermodegradable layer is thereby heated to its degradation temperature and the areas thereof in contact with the heated metal zones are destroyed to provide an information bit.
In U.S. Pat. No. 4,032,691, there is disclosed an optical disk comprised of a recording layer of a metal, dye and/or synthetic resin, and a thermally insulating base layer. To increase the sensitivity of the recording material, the patent proposes to use a porous layer between the support and the recording layer.
The use of bubbles, or vesicular materials, in optical disks has also been suggested. For example, in an article by R. P. Freese et al entitled "Characteristics of Bubble-Forming Optical Direct-Read-After-Write (DRAW) Media", SPIE, Vol. 329 Optical Disk Technology (1982), there is described a trilayer thin film construction useful in optical disks. The top layer consists of a thin, tough film of a refractory material. The middle layer is an optical spacer of either organic or inorganic material. The bottom layer is a reflective metallic film, such as Cr, Al, Ti or Cu. When the media is exposed to a well focused laser beam, a protuberance or bubble is formed. This formation of the surface protuberance destroys the anti-reflectance condition of the trilayer stack, thus enabling a high reflectance contrast readout of the information.
In "Textured Surfaces: Optical Storage and Other Applications", by Craighead et al, J. Vac. Sci. Technol., Vol. 20 (3), March 1982, there is also disclosed the use of textured surfaces and the selective melting thereof to form smooth reflective regions which can be read as recorded information.
Despite all of the foregoing techniques for the optical recording of information on media such as disks, cards or tapes, the search for a low cost, low energy approach (i.e., more energy efficient approach), particularly as compared to ablative hole burning in metallic layers or dye/polymer layers, is continually on-going. Moreover, there is a need of such an energy efficient system which also provides a high signal to noise ratio. In order to have commercial acceptability, a high signal to noise ratio in read-out of the information is very important.
Accordingly, it is a major objective of the present invention to provide a novel optical recording medium which is stable and on which information can be readily and effectively recorded with a low expenditure of energy, and read with an enhanced signal to noise ratio.
It is yet another object of the present invention to provide a novel recording medium upon which information is recorded as a transparent region.
It is still another object of the present invention to provide a recording medium which comprises a microporous polymeric layer whose structure will selectively and controllably be collapsed to provide a recordation of information.
It is still another object of the present invention to provide a recording disk, card or tape comprising a uniquely suited polymer layer which renders the recording of information technically accurate, economically expedient and energy efficient, with a high signal to noise ratio being exhibited upon reading the information.
Yet another object of the subject invention, in general, is to provide a novel method of recording information by using a microporous polymer layer as an information layer.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the appended claims.